Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 30-01-2021, 14:29   #1
Registered User

Join Date: Dec 2015
Location: Minnesota
Boat: Vaitses/Herreshoff Meadow Lark 37'
Posts: 849
How much ventilation for diesel?

I have a boat with a Yanmar 3GM30, that had it's engine compartment vents removed for painting.

I could simply replace what was there, but I'm not really thrilled with the location or design.

But before I do anything different, where could I find out how mugggch air intake a 3GM30 requires?

And how large a vent area would be required to provide this?
Jdege is offline   Reply With Quote
Old 30-01-2021, 14:55   #2
Registered User
 
flyingfin's Avatar

Join Date: Oct 2016
Location: Cape Haze,FL
Boat: Carver,Cobia,Nacra, Columbia
Posts: 766
Re: How much ventilation for diesel?

Look at your car engine, what size is the intake just before the air filter? Not very big!
flyingfin is offline   Reply With Quote
Old 30-01-2021, 15:17   #3
Marine Service Provider

Join Date: Sep 2014
Location: Auckland, NZ
Boat: Compass 790 , 7.9 metres or 26 ft
Posts: 2,608
Re: How much ventilation for diesel?

Quote:
Originally Posted by flyingfin View Post
Look at your car engine, what size is the intake just before the air filter? Not very big!

Depends if his car is petrol or diesel.
Diesels require roughly twice as much air as the same cc petrol engine, the clue is in the compression ratio.
Compass790 is offline   Reply With Quote
Old 30-01-2021, 15:47   #4
Registered User
 
Reefmagnet's Avatar

Join Date: May 2008
Location: puɐןsuǝǝnb 'ʎɐʞɔɐɯ
Boat: Nantucket Island 33
Posts: 4,652
Re: How much ventilation for diesel?

I've been concerned (rightly or wrongly) about the effects of drawing air for the engine from the sound proofed engine bay (which also acts to insulate it) as this is a very 1970's approach with inherent lack of efficiency so the first question is are you running ducts to the vents? If so the area would need to be at least the same as the air intake on the engine, preferably a little more.



If you're simply drawing the air from the engine compartment then it's unlikely to be totally hermetically sealed so air will flow in from every gap, particularly the bilge area (which will also have plenty of subtle openings), and this is probably more than adequate for the supply to the engine. If this is the case, you may find the purpose of the vents is to actually help discharge heat from the area once the engine is stopped.
Reefmagnet is online now   Reply With Quote
Old 30-01-2021, 16:05   #5
Registered User
 
Uncle Bob's Avatar

Join Date: May 2010
Location: Sydney Australia
Boat: Fisher pilothouse sloop 32'
Posts: 2,568
Re: How much ventilation for diesel?

Quote:
Originally Posted by Compass790 View Post
Depends if his car is petrol or diesel.
Diesels require roughly twice as much air as the same cc petrol engine, the clue is in the compression ratio.

Sorry old mate, I have to disagree with you on this one, The air capacity of any engine is dependant on the bore x stroke x rpm. Any two engines of a comparable size will draw similar volumes when run at similar revs, sure a diesel has approx double the compression rate, this is a function of piston crown height to cylinder head. Running higher compression ratios possibly increases internal losses down the bore than a lower compression engine, and coupled with the fact that diesels run slower than petrol engines, it is probable that the diesel in fact uses less air than the petrol equivalent.
The exception would be if the diesel was a turbo model.
__________________
Rob aka Uncle Bob Sydney Australia.

Life is 10% the cards you are dealt, 90% how you play em
Uncle Bob is offline   Reply With Quote
Old 30-01-2021, 16:11   #6
Moderator
 
Pete7's Avatar

Cruisers Forum Supporter

Join Date: Aug 2009
Location: Solent, England
Boat: Moody 31
Posts: 15,733
Images: 14
Re: How much ventilation for diesel?

Quote:
Originally Posted by Uncle Bob View Post
Sorry old mate, I have to disagree with you on this one, The air capacity of any engine is dependant on the bore x stroke x rpm.
Divided by 2 for a four stroke engine surely?
Pete7 is online now   Reply With Quote
Old 30-01-2021, 16:15   #7
Registered User

Join Date: Dec 2015
Location: Minnesota
Boat: Vaitses/Herreshoff Meadow Lark 37'
Posts: 849
Re: How much ventilation for diesel?

It's my Herreshoff/Vaitses Meadow Lark.

The engine is under the cockpit, and there are two 4-inch holes on the outside coamings, and simple clamshell vent covers for them.

I'm thinking I'd like something that would make it more difficult for water to get in, but as I consider alternatives I need to know actual requirements.
Jdege is offline   Reply With Quote
Old 30-01-2021, 16:17   #8
Registered User
 
Uncle Bob's Avatar

Join Date: May 2010
Location: Sydney Australia
Boat: Fisher pilothouse sloop 32'
Posts: 2,568
Re: How much ventilation for diesel?

Quote:
Originally Posted by Pete7 View Post
Divided by 2 for a four stroke engine surely?

I guess that technically, yes, however the simple reality is that an engine running at x rpm will consume y cfm of free air.
__________________
Rob aka Uncle Bob Sydney Australia.

Life is 10% the cards you are dealt, 90% how you play em
Uncle Bob is offline   Reply With Quote
Old 30-01-2021, 16:18   #9
Marine Service Provider
 
Emmalina's Avatar

Join Date: Jan 2012
Location: Thailand
Boat: Herreshoff Caribbean 50
Posts: 864
Re: How much ventilation for diesel?

If the mfct put vents in they were probably required they don't do things for fun !
__________________
Steve .. It was the last one that did this !
Emmalina is offline   Reply With Quote
Old 30-01-2021, 16:18   #10
Registered User

Join Date: Mar 2020
Location: Wherever we please, GOM
Boat: 46 ft cutter
Posts: 172
Re: How much ventilation for diesel?

Compression ratio matters. Gasoline (petrol) engines run about 8:1 compression ratio. Diesels often run 20:1 or higher.

IE they consume 2,5 times (or more) air
PirateGuy is offline   Reply With Quote
Old 30-01-2021, 16:31   #11
Registered User
 
Uncle Bob's Avatar

Join Date: May 2010
Location: Sydney Australia
Boat: Fisher pilothouse sloop 32'
Posts: 2,568
Re: How much ventilation for diesel?

Quote:
Originally Posted by PirateGuy View Post
Compression ratio matters. Gasoline (petrol) engines run about 8:1 compression ratio. Diesels often run 20:1 or higher.

IE they consume 2,5 times (or more) air

Then could you please explain just how a piston running up and down in a bore at a given speed can use 2.5 times more air if it is diesel rather than petrol. Yes the compression ratio is approx 2.5 times higher, however compression is a function of how close the piston crown is to the cylinder head at the top of the stroke.
__________________
Rob aka Uncle Bob Sydney Australia.

Life is 10% the cards you are dealt, 90% how you play em
Uncle Bob is offline   Reply With Quote
Old 30-01-2021, 16:39   #12
Marine Service Provider

Join Date: Sep 2014
Location: Auckland, NZ
Boat: Compass 790 , 7.9 metres or 26 ft
Posts: 2,608
Re: How much ventilation for diesel?

Quote:
Originally Posted by Uncle Bob View Post
Sorry old mate, I have to disagree with you on this one, The air capacity of any engine is dependant on the bore x stroke x rpm. Any two engines of a comparable size will draw similar volumes when run at similar revs, sure a diesel has approx double the compression rate, this is a function of piston crown height to cylinder head. Running higher compression ratios possibly increases internal losses down the bore than a lower compression engine, and coupled with the fact that diesels run slower than petrol engines, it is probable that the diesel in fact uses less air than the petrol equivalent.
The exception would be if the diesel was a turbo model.

Yes quite right.
I was assuming that capacity was volume measured at TDC.
WRONG! It is bore x stroke.
Old age brain fart.

Thank you for straightening that out.
I feel a bit like the NYYC now.
Compass790 is offline   Reply With Quote
Old 30-01-2021, 16:42   #13
Registered User

Join Date: Dec 2015
Location: Minnesota
Boat: Vaitses/Herreshoff Meadow Lark 37'
Posts: 849
Re: How much ventilation for diesel?

Quote:
Originally Posted by Emmalina View Post
If the mfct put vents in they were probably required they don't do things for fun !
It's a 40-year-old boat.

Who knows what the manufacturer did?

I do know that the Yanmar isn't the original engine.
Jdege is offline   Reply With Quote
Old 30-01-2021, 16:46   #14
Registered User
 
Cheechako's Avatar

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 24,118
Re: How much ventilation for diesel?

I think most boat makers rely on ill fitting hatches and enclosures to provide the air. I often see no intake but often see exhaust fan outlets.
Some engine makers will specify how much open intake is required. I guess you don't want the engine sucking too hard. More suck=more velocity=more air.
But even on a small boat with two 6 cyl Cummins diesels it wasn't a lot. Thinking back maybe 8" x 48"

I imagine whatever the engine intake size is will work, if ducted maybe a little more, if free to breathe without a duct, just an opening that size..
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 30-01-2021, 16:54   #15
Registered User

Join Date: Jan 2015
Location: SoCal
Boat: Formosa 30 ketch
Posts: 856
Re: How much ventilation for diesel?

A diesel engine inhales about 1/2 its displacement per revolution, a gas engine running 7 inches of vacuum inhales only half as many molecules per revolution.
Bill Seal is offline   Reply With Quote
Reply

Tags
diesel

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How much water in diesel is to much? andreas.mehlin Engines and Propulsion Systems 33 18-12-2018 06:02
How much ventilation for solar controller? Wanderlust Electrical: Batteries, Generators & Solar 4 14-05-2013 11:48
Diesel Fumes & Ventilation raycoker Engines and Propulsion Systems 3 17-04-2012 18:00
Multihull Ventilation? gbanker Multihull Sailboats 9 21-12-2006 16:25
Battery Ventilation when ‘Fast’ Charging GordMay Electrical: Batteries, Generators & Solar 20 05-04-2006 12:27

Advertise Here


All times are GMT -7. The time now is 06:40.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.